1. Field of the Invention
The present invention relates to a tubular film die head for extruding single-layer or multi-layer film having a substantially annular die gap, fastening elements which fix at least two components with respect to one another which together border areas bearing plastic melt within the tubular film die head, and coolant-carrying elements.
2. Description of the Related Art
The extruded tubular films find use in the packaging material industry, among others.
Tubular film die heads of the type cited are, for example, shown in EP 0 626 247 A1, U.S. Pat. No. 5,069,612, and in DE 100 01 363 A1. In all the tubular film die heads of this type there is the necessity of distributing plastic melt, which is conveyed in the lines, within the die head so that it reaches an annular die gap relatively uniformly. In this way the plastic melt is formed into a film tube.
Among other things, for reasons of manufacturing technology (of the die head), at least one part of the distribution process of the plastic melt is, as a rule, done by plastic melt-carrying areas which are bounded by at least two components. The aforementioned publications show that the geometric structure of these areas can be realized in the most varied forms.
Due to the substantial pressure which the melt is under, forces act on these components, often called lifting forces. Among other things, these forces must be absorbed by robust fastening elements which often have a not insignificant demand for volume.
After extrusion, the film tube is conveyed as a rule to a squeezing device and later to a reversing device. This state of affairs, such as the reel of the die head, squeezing roller, and reversing are known and represented by EP 0 873 846 A2, among others.
Due to this situation the film tube is closed from above and from the sides. Thus, for example, the intake and discharge of coolants, such as, for example, coolant air for the cooling of the interior of the tube, must be done through the die head. Since the lines for feeding the plastic melt, fastening elements, and electric lines for sensor and heating elements and the like must also be conducted through the die head, the design of the die head becomes extraordinarily complicated. In particular, U.S. Pat. No. 5,538,411 shows the complexity of the die head design. In this publication fastening elements as well as coolant lines are shown, among other things.
Often the arrangement of said lines is done at the expense of the height of the die head. However, the height should actually be kept very small in order to protect the plastic melt.
Thus, the publications U.S. Pat. No. 4,003,972, U.S. Pat. No. 3,471,899, and GB 1 253 454 shows die heads in each of which a fastening element with a coolant line is provided. The die head patented in DE 100 48 862 C2 is to be considered as a further development of this type of die head which comprises a fastening element in which two coolant lines are integrated. Due to these two integrated coolant lines such a fastening element assumes a significant volume.